Various types of inhaler are known and widely used on the market. For example, many asthma sufferers regularly use a spray inhaler comprising a gas propellant which is stored in a metal container containing additionally a medicinal substance to be inhaled to ease the cause and or symptoms of the affliction. The metal container is connected in use to a hollow plastic carrier which at one end has a mouthpiece for the user. The device is operated by pressing the metal container inwardly with respect to said plastic carrier to thus release a pressurised dosage of medicine.
Such devices are however bad for the environment due to the use of propellants and other carrier gases. Additionally the amount of medicament which is inhaled comes from a store of medicine in the container suitable for many inhalations, such that considerable problems arise concerning the amount of each dose inhaled due to incomplete or uneven mixing of the medicament, or due to variations in the available gas pressure. Further dosage anomalies may also occur if the inhaler has been allowed to stand for a long period of time between uses. Moreover such inhalers are relatively bulky and expensive.
Also known are inhalers which have a body portion containing an impeller blade or fan incorporated therein and further including a compartment for the introduction of a medicament. On operation, said medicament is ejected by the action of the rising air flow caused by the fan.
Such inhalers have the disadvantage that an uneven flow often results and the construction of the device makes it relatively expensive, bulky and prone to breakage or malfunction.
A further known inhaler having the features defined in the preamble of claim 1 is disclosed in U.S. Pat. No. 4,069,819. The inhaler device of this document however presents difficulties in normal operation because powder is withdrawn slowly from the capsule within the capsule chamber, partly due to the small diameter of the holes which are possible in the capsule due to the design of the device and partly due to the limited movement of the capsule in the chamber. The capsule is restrained in the longitudinal direction by an intermediate wall containing a plurality of holes and comprising a semi-spherical lower surface which is on a wider arc than that of the capsule upper end to thereby allow rotational procession of the capsule thereagainst without substantial hindrance, whilst still allowing powder to reach the user.
The powder entering the mouthpiece is thus confined to a substantially laminar flow such that the dispersion/separation thereof is minimal and the sucking effort required will often be quite large. Moreover one or more of the plurality of passages will often be blocked by the capsule leading to particle build-up and clogging.